Process for fluid calcining cement raw meal

ABSTRACT

A new process for fluid calcining cement raw meal using a fluidized furnace equipped between a rotary kiln and a suspension preheater and having a separate heat source is provided. This process comprises dividing an air stream to be fed into the fluidized furnace into two parts and introducing one part thereof into a fluidized bed of the fluidized furnace and the other part thereof into a space above the fluidized bed for the purpose of increasing a calcining capacity of the fluidized furnace and at the same time reducing a running cost thereof remarkably.

United States Patent 11 1 [11] 3,873,331 Kondo et al. [45] Mar. 25, 1975[5 1 PROCESS FOR FLUID CALCINING 2.776,]32 1/1957 Pyzel l06/l00 E E WMEAL 3:32; :yze: $2188 [75] inventors: Marekata Kondo,Yono;Seiwa yze IFukuda, Kawagoe; Toyohlko Yamamoto, Omiya, all of Japan j y gr mar-1 1PoerEd d J B i 731 Assignee: Mitsubishi Mining & Cement war rennetCompany. Ltd., Tokyo, Japan 22 Filed: Aug. 22. 1913 1511 ABSTRACT ppl-N03 A new process for fluid calcining cement raw meal using a fluidizedfurnace equipped between a rotary [30] Foreign Applkmon Prior), Dam kilnand a suspension preheater and having a separate Au 3] I972 J3 an 4786612 heat source is prov1ded. Th1s process compnses d1v1d p ing an airstream to be fed into the fluidized furnace into two parts andintroducing one part thereof into a 6 gg2 fluidized bed of the fluidizedfurnace and the other [58] Field 432/15 part thereof into a space abovethe fluidized bed for the purpose of increasing a calcining capacity ofthe fluidized furnace and at the same time reducing a run- [561 UNITEBS?X:ES SZ TENTS ning cost thereof remarkably.

2.409,?07 l0/l946 Roetheli 106/100 1 Claim, 2 Drawing FiguresPATENTEDHARZBWS combustion rat: in fluidized bed. 94)

.FtQL 1' l I\l\I \]Q- r .17: J9 7 A I J; I 1 x15 5 J5 if .11 I 10 J2fuel ioad. f7 90 PROCESS FOR FLUID CALClNlNG CEMENT RAW MEAL BACKGROUNDOF THE INVENTION This invention relates to a process for fluid calciningcement raw meal which uses a fluidized furnace equipped between a rotarykiln and a suspension preheater and having a separate heat sourcecomprising dividing a part of an air stream to be fed into the fluidizedfurnace and introducing it into a space above a fluidized bed of thefurnace for the purpose of increasing a calcining capacity of thefluidized furnace and reducing a running cost thereof remarkably.

A process for burning cement clinker (Japanese Pat.

Publication No. 30058Il968) comprising a fluidized furnace as a calciner(said fluidized furnace is referred to hereinafter as a fluidizedcalciner) equipped between a rotary kiln and a suspension preheater andhaving a separate heat source is, as is generally known. an inventionwhich solves problems including a short life comprising dividing an airstream to beintroduccd into said fluidized furnace into two parts andintroducing one part thereof into a fluidized bed of said furnace andthe other part thereof into a space above said fluidized bed.

The features of this invention reside in that an air stream to be fedinto a fluidized furnace is divided into two parts, one part thereofbeing introduced into a lowof refractory materials due to the increasedheat load above, however it is well-knowntheoretically and cmi piricallythat in the case in which as a combustion mechanism mainly a combustionin the fluidized bed is considered. it is necessary to keep the heightof the fluidized bed high so as to have a heat load increased. Further,air fed into said fluidized bed is air for fluidizing and at the sametime air for combustion of fuels. As there is a limitation on the amountof the air for fluidizing. the amount of a burnable fuelsupplied. thatis. a heat load which said fluifized calciner can bear is spontaneouslylimited. t

As is generally known. in order to operate a fluidized furnaceeconomically. it is desirable to reduce a running cost thereof bykeeping the height of a fluidized bed as low as possible to make apressure loss of the fluidized bed decreased and at the same time makethe equippment small-sized or a treatment capacity thereof increased byincreasing the heat load.

This invention has been devised to overcome the de-' ered fluidized bedof said furnace and another part thereof being introduced into a spaceabove the fluidized bed to carry out positively a combustion in saidspace. thereby cnablinga reduction power eomsumptionforlair forcedfeeding and an increase of a heat load. i

These and otheriobjects of this invention will be readily appreciated byreference to the following detailed description when considered inconnection with the accompanying drawing.

BRIEF DESCRlPTlON OF THE DRAWING HO. 1 is an arrangement drawing ofacement clinker burning equippment with a fluidized calciner equippedbetween a rotary kiln and a suspension prchcater and having a separateheat source used for carrying out a preferred embodiment of thisinvention.

FIG. 2 is a graph showing a relation between a height of the fluidizedbed plotted as abscissa and a combustion rate in the fluidized bedplotted as ordinate at various fuel loads.

DETAILED DESCRIPTION OF THE lNVENTlON This invention comprises burningonly the part of the bed, cracking at the same time the whole remainingformly the fuel gasgcnerated by said cracking in the fects of theconventional fluidized calciner as described hereinabove.

SUMMARY OF THE lNVENTlON A primary object of this invention is toprovide a process for fluid calcining cement raw meal which makes a heatload of a fluidized calciner increased. thereby enabling an increase incalcining capacity thereof.

Another object of this invention is to provide a process for fluidcalcining cement raw meal which makes a pressure loss due to a fluidizedbed decreased, thereby enabling a reduction of running cost of the fluidized calciner.

A further object of this invention is to provide a process for fluidcalcining cement raw meal which prevents the generation of coatingtrouble in the fluidized calciner, thereby enabling a stable operationthereof.

According to this invention. there is provided a process for fluidcalcining cement raw meal using a fluidized furnace equipped between arotary kiln and a suspension preheater and having a separate heatsource,

part of the fuel in said bed, burning rapidly and unispace above thefluidized bed with the air stream divided introduced into said space soas to have the cement raw meal floating uniformly and in highconccntration in said space effectively calcined.

According to the relation between a height of the fluidized bed and acombustion rate inthe fluidized bed at various fuel loads (H6. 2)obtained in the research process of this invention. it was confirmedthat although it is required to increase the height of the fluidized bcdso as to have the combustion rate in said bed improved. increasinglyblindly the height of the fluidized bed is not preferable from anoperational point of view because the pressure loss of the fluidized bedbecomes extensive and the combustion rate is not so improved for theincreased height of the fluidized bed. Es-

pecially in the case in which cement raw meal is cal cined by means ofthe fluidized bed. such a process comprising burning only the part ofthe fuel fed into the.

fluidized bed which is burnable in said bed therein. cracking the wholeremaining part of said fuel in said bed and carrying out positively acombustion above said bed as this inventionwas confirmed to be more favorable than a process which is mainly based on a combustion in thefluidized bed having it increased height for the reason that a heat loadper unit sectional area of the fluidized furnace can be increased morethan the combustion capacity in the fluidized bed and/or in all- 3 overpower consumption for air feed can be decreased by introducing acombustion air divided into the space above the fluidized bed having apressure as low as the atmospheric pressure and simultaneously makingthe of an all'over height of the fluidized bed as low as possible so fara stable fluidized state can be kept.

The reason that such a combustion above the fluidized bed as describedhereinafterjis safely possible especially in the case in-which cementraw meal is cal ,cincd was confirmed by the operation research asfollows. r

First, in the method for burning fuels according to this invention. inwhich a fluidized bedis utilized as a cracking means for the remainingpart of the fuel which uses caloric power of the fuelburned in said bedas a heat source. a dispersion of the fuel gasified by said crackinginto the space ubove the fluidized bed is ideally uniform and a fueldensity in said space becomes small. such a local high temperature flameas seen in a space combustion by means of an ordinary burner is s notformed. Therefore. there is generated no coating trouble due to anadhesion of low melting temperature bustion rate in the fluidized bed ofthe fuel fed. that is.

the height of the fluidized bed. in this case. it is possible to setupthe temperature of the fluidized bed independentlyof the decarbonizationtemperature of the raw meal and it isalso ossihle too crate nde th d'- Il i u f n i calctned.aparttcle stze distribution of the former beingtion-in which the temperature of the fluidized bed is lower than thedeearbonization equilibrium temperature.

Secondly. about 70 percent of the raw meal calcined which is dispersedintothe space above-the fluidized bed uniformly and in highconcentration by the fluidized bed. comprises carbonatesalts. and thesedecarbonization reactions proceed at about 800-850C. accompanying agreatdeal of heat absorption of about Sl QkcaIIkg clinker includingdehydration heat of kamentio'ned. the combustion heat of the fuel burnedin the space above the fluidized bed is immediately supplied to thesedeearbonization reactions. therefore the temperature of the fluidizedcalciner waste gas he comes llStl'-9(l(lC slightly higher than thedecarhonization'temperature. thereby making the raw meal very I g Theeffect of this invention is that a heat load per unit sectional area ofthe fluidized bed can be increased in proportion to the amount of airintroduced into the space above the fluidized bed and owing to such alow pressure in the space above the fluidized bed as anatmosphericpressure the air stream divided can be blown into said spaceeven by a low pressure fan. therefore an all-over air pressure can bedecreased remarkably. as compared with the conventional process. eventhough the fluidized calciner is operated at the same pressure loss ofthe fluidized bed as that of the conventional process. 1 i i Thisinvention will now be illustrated by the following example. Of course.this invention shall not be limited to the following example.

EXAMPLE FIG. I is arrarrangement drawing of a cement clinker burningequippment with a fluidized calciner equipped between a rotary kiln anda suspension preheater and a having a separated heat source used forcarrying out this Example. This fluidized calciner comprises introducingan air stream divided into a spaceabove a fluidized bed so as to have acombustion above the fluidized to bed carried out positively. i i f inH6. 1. l is a raw meal feeder. 2 a suspension PFC- r I heater, 3 aninduced draft fan. 4 a rawmcal chute for a fluidized calciner. 5a-fluidized culcinerro hunters for a fluidizedcalciner. a waste gas ductof a fluidized l5 calciner, 8 a smoke chamber of a rotary kiln. 9 arotary kiln waste gas duct, 10 a raw material chute. II a rotary kiln,12 a' clinker cooler, 13 arotary kiln burner. l4 a dust collectorfor aclinker cooler waste gas. 15 a fluidization blower. 16 a fluidizingunit. 17 a fan for a (lll vided air stream. 18 a fluidized bed. andil 9a space above afluidized bed.

i A part or a whole quantity of the raw meal already partially calcinedby heat-exchange with the hot gas in the preheater 2 is extracted fronta suitable place. for

example. from a raw material outlet of a cyclone. just above the loweststage cyclone of the preheater 2 to he introduced through the raw mealchute-4 into the fluid- Q izedcalciner 5. in this Example. the fluidizedbed is composed of-a fluidizing medium and a raw meal to be notoverlapped with that of the latter; anda method of discharging the rawmeal from the fluidized calciner is a carry over systemin which thewhole quantity of the raw meal calcined is accompanied by the fluidizedcalciner wste gas. 7 i p I y r The extracted gas or waste gas of ISU3SQCfrom the clinker cooler 12 is treated by the dust Collector 14 and thenis divided into two parts, a part-thereof being introduced through thefluidizing unit 16 into the fluid- 1 ized bed 18 by means of the blower15 so asto have flu ohnc. Furthermore. as these decarbomzatton reactionsI proceed very rapidly at the temperature range above idizing mediumvigorously fluidized. This waste gas substantially comprising air takespart in a combustion of a part of the fuel fed by the burners 6. and atthe same time disperses the raw meal in the fluidized bed. I after itsresidence therein for a certain time. into the space 19 abovethefluidized bed 18. On the other hand. as another part of said clinkercoolerwaste gas divided is blown into the space l9 above the fluidizedbed 18 through one inlet or plural ones almost tangen tially by the fan17. a fuel gas generated by cracking of the fuel in the fluidized hedis-uniformly andrapidly burned in the space 19 above thefluidized bedl8. As

the dispersion of the raw meal is very good and the fuel is crackeduniformly in the whole fluidized bed.- there occurs neither localoverheatingdu e to local flames.

nor coating trouble due to an adhesion of low. melting components ofth'eraw meal;

The whole quantity of the raw meal calcined accom-j panied by thefluidized calciner waste gas is entered 8 to he mixed with the rotarykiln waste gas therein. then is inthrough the duct 7 into the smokechamber troduced through the duct 9 into the lowest stage cyclone of thepreheater 2. and if required. with the rentaining part of the raw mealnot introduced into the fluidized calciner 5. to he calcined therein bythe high temperature rotary kiln waste gas and then collected by saidcyclone. and is finally introduced through the raw meal shute into therotary kiln 11 to be burned to a this invention process and those of theconventional process is shown inthe following table ing thereof iscarried out, therefore this invention is in- ,5 using a separate heatsource combined with a suspenheightof mama calcining 'air abovefluidized bed ratio temperature fluidized bed ratio mm I. r J C I I i200no 1 850 40 ll 1 lSZ 850 a 55 Ill I I00 850 p 0 power consumption fordccarbonization treatment capacity air forced feeding rate 2 w ratto 2'itwHlt CllllkCl inlet outlet l 1.2 8.l auj l6! ll 1.0 a 8.l 86.8 142 m2.5 p 8.2 l 89.; p i :00

notes: (I) l. ill this invention process lll the conventional process(-2) fuel load ratio and treatment capacity are regarded as nm in theconventional pm cess The case i is a case of this invention process inwhich the height of the fluidized bed is the same as that of the caseill of the conventional'process, in the case i. the 3 increase in thefuel load dueto the combustionabove the fluidized bed isabout 70percentand the decrease sion preheating type cement clinker burning process.

the improvement comprising in the'all-over power consumption for airforced feeding due to the increase of the treatment capacity is about S0percent. as compared with the case llLThe case ii is a case of thisinvention process in which the height of the fluidized bed is half ofthat of the case ill.

7 In the case II. the increase in the fuel load is about 52 percent andthe decrease in the all-over power con ventional process andconsequently a e fl ect ive calcin;

' sumption for air forced feeding due to both the lowered regulating theheight of a fluidized bed as low as possible while {maintaining saidbed' in a stabilized state. said bedconsisting mainly of a fluidizingmedium and cement raw meal and the particle size distribution of saidfluidizing medium being not overlapped with that of said cement raw mealdividing an air stream intotwoparts.

introducing one part of said air stream into said fluidized bed so as toburn fuel charged thereinto and to gasify the remainder of said fueltherein with heat generated by said burning of the fuel. and introducingthe other part of said air stream intoa space above said fluidized bedto burn said gasilicd fuel dispersing uniformly in dilutedconeentrationin said space for calcining said cement raw meal floating in denseconcentration therein.

1. IN A PROCESS FOR FLUID CALCINING CEMENT RAW MEAL USING A SEPARATEHEAT SOURCE COMBINED WITH A SUSPENSION PREHEATING TYPE CEMENT CLINKERBURNING PROCESS, THE IMPROVEMENT COMPRISING REGULATING THE HEIGHT OF AFLUIDIZED BED AS LOW AS POSSIBLE WHILE MAINTAINING SAID BED IN ASTABILIZED STATE, SAID BED CONSISTING MAINLY OF A FLUIDIZING MEDIUM ANDCEMENT RAW MEAL AND THE PARTICLE SIZE DISTRIBUTION OF SAID FLUDIZINGMEDIUM BEING NOT OVERLAPED WITH THAT OF SAID CEMENT RAW MEAL, DIVIDINGAN AIR STREAM INTO TWO PARTS, INTRODUCING ONE PART OF SAID AIR STREAMINTO SAID FLUDIZED BED SO AS TO BURN FUEL CHARGED THEREINTO AND TOGASIFY THE REMAINDER OF SAID FUEL THEREIN WITH HEAT GENERATED BY SAIDBURNING OF THE FUELM AND INTRODUCING THE OTHER PART OF SAID AIR STREAMINTO A SPACE ABOVE SAID FLUDIZED BED SO AS TO BURN SAID GASIFIED FUELDISPERSING UNIFORMLY IN DILUTED CONCENTRATION IN SAID SPACE FORCALCINING SAID CEMENT RAW MEAL FLOATING IN DENSE CONCENTRATION THEREIN.